A lead frame forms the base or skeleton of an IC package, providing mechanical support to semiconductor dies during assembly into a finished package. A lead frame typically includes bonds pads such as die paddles for attaching semiconductor dies and leads for providing external electrical connections to the dies. The dies can be connected to the leads by wires, e.g. through wire bonding or tape automated bonds. Lead frames are typically constructed from flat sheet metal, e.g. by stamping or etching. The sheet metal is typically exposed to chemical etchants that remove areas not covered by photoresist. After the etching process, the etched frames are singulated (separated) into lead frame strips. Each lead frame strip includes a number of unit lead frames each having the bond pad construction described above.
Semiconductor dies attached to the die paddles after completion of the assembly process of a lead frame strip are usually tested after separation of the unit lead frames from the lead frame strip. Alternatively, the unit lead frames remain mechanically connected to the lead frame strip by tie bars during die testing. This is commonly referred to as lead frame strip testing. Separation of the unit lead frames from the lead frame strip occurs after electrical testing. In either case, the lead frame strips are then over-molded to form encapsulated individual packages which are then singulated (divided) into physically separate packages. The package singulation process conventionally involves sawing through the molding compound and the metal tie bars which electrical conductor adjacent bond pads for increased lead frame stability during earlier processing. Sawing through thick tie bars causes mechanical stress, and in the case of copper lead frames, copper burrs and copper particulate contamination. These issues can be reduced by slowing the sawing speed from 300 mm/s to 50 mm/s and providing a stronger spray to remove the copper particulates. However, such modifications to the singulation process increase the overall package cost due to the 2× slower sawing time and also decrease tool throughput.